Birth Defects - Genetic - Down Syndrome

Down Syndrome

Down's syndrome, also referred by some, as 'Mongolism' is a genetic condition that arises due to an extra copy of all or part of chromosome 21. The condition was named after Langdon Down who first described this syndrome.

Children with Down syndrome have delayed milestones. Most exhibit poor cognitive skills, but many of them learn several skills during their lifetime.

There are several prenatal tests that may be carried out on high-risk mothers to detect a Down syndrome fetus. They are-

• Detailed Ultrasound
• Nuchal translucency test
• Triple screen or the multiple marker test
• Amniocentesis
• Percutaneous umbilical cord sampling
• Chorionic Villi sampling

A karyotyping done on a blood sample from a Down syndrome individual will help to confirm the diagnosis.

Down syndrome cannot be cured but thankfully many of the clinical symptoms of this disorder can easily be managed. Several affected individuals lead near-normal lives.

Incidence

1 in 600 - 1 in 800

Cause

Down syndrome is the most common autosomal aneuploidy. An alteration in the number of 46 chromosomes in a cell, either by a loss or a gain of chromosomes is called aneuploidy. In Down syndrome there is an extra copy of the chromosome 21.

Advanced maternal age (> 35 years) is found to be associated with an increased risk of Down syndrome.

Clinical features:

• Slanted eyes with epicanthal skin folds
• White spots on the iris (Brush field spots)
• Small folded ears
• Flat nasal bridge
• Open mouth
• Protruding tongue
• Short neck
• Short hands and feet
• Simian crease on the palm,
• Low level of intelligence, sometimes severe form of mental retardation observed
• Duodenal obstruction
• Skin disorders

• Thyroid problems
• Pulmonary hypertension
• Poor muscle tone
• Incompetent immune system
• There is a greater risk of acute leukemia in these individuals
• Absence or closure of anus, esophagus or duodenum,
• Eye disorders
• Increased susceptibility to upper respiratory tract infections
• Congenital heart defects
• Males with the disorder are sterile. Females with the syndrome can conceive, but the risk of Down syndrome in child is 50 %.

Life expectancy

Death may occur in the first year of life due to congenital heart defects.

• 20 % - die at age 5
• 75-80 % die at age 10
• 25 % - die at age 20

But many of these individuals become adults and are capable of leading a normal life. They can be trained to be independent, with some of them even being able to go for jobs.